Atrial flutter.

was attempted in eight patients with drug refractory type I atrial flutter. In seven of eight patients, a zone of prolongation and fragmentation of the endocardial electrogram was found in the low posterior part of the right atrium. Entrainment of the atrial flutter by high right atrial pacing was accompanied by local recording of second-degree regional block in several atrial sectors but never in the low septal area. We, therefore, hypothesized that the latter represented the critical slow conduction zone of the reentrant flutter circuit. One or two cathodal DC shocks were locally delivered without immediate or late complications. One single ablation attempt was performed in five patients, whereas three patients underwent a second attempt because of early flutter recurrence. Patients were initially discharged without (and after a second session with) antiarrhythmic drugs. After a mean follow-up of 15.5 months (range, 10-23 months), five patients are free of arrhythmias without antiarrhythmic drug therapy. Two patients did not experience atrial arrhythmias while on a drug regimen that was previously found to be ineffective, and a third patient had flutter recurrences. This study suggests that patients with type I atrial flutter referred for atrioventricular node-His bundle ablation may be successfully managed by delivering the ablative shock directly on the atrial arrhythmia substrate. (Circulation 1990;81:762-771)